The increasing demand for high-speed data communications and broadband access to computer networks such as the Internet is creating a corresponding demand for additional network bandwidth. In many cases, increasing the available bandwidth involves deploying fiber optic networks to replace older, slower transmission media. Additionally, current efforts by many businesses, government agencies, educational institutions, municipalities and the like involve creating and/or expanding existing fiber optic networks to reach additional end-users.
Extending the fiber optic transmission line beyond the backbone and to the final point of end-user access generally requires a relatively significant increase in the number of optical terminations or optical transceivers on the network. These transceivers may be termed “Fiber To The X” transceivers or “FTTX” transceivers where the “X” represents a final termination point for one part of the fiber optic network. One type of FTTX transceiver, a single fiber implementation, comprises a 1.3 micron laser light source and a 1.55 micron detector/amplifier. These single fiber FTTX transceivers use the same fiber to receive and detect 1.55 micron light signals and generate 1.3 micron light signals in return. It should be noted that other types of FTTX transceivers are in use, many of which use one fiber to receive signals and another fiber to send signals.
Manufacturing these FTTX transceivers typically involves fabricating a coupling structure that simultaneously couples the 1.3 micron laser to the fiber and re-directs the in-coming 1.55 micron light to the detector/amplifier. Many FTTX transceivers are implemented using planar technologies including waveguide structures that separate the incoming 1.55 micron light signal from the outgoing 1.3 micron light signal so that optical crosstalk between the 1.55 micron detector/amplifier and 1.3 micron laser is kept as low as possible. Other implementations include edge-emitting waveguide coupled lasers, waveguide-coupled detectors, and spot size converters that convert the fiber modes into relatively compact semiconductor waveguide modes and back again.
Several different technologies have been employed to manufacture these various FTTX transceivers. First, some transceivers have been built using the component and packaging technology previously developed in conjunction with the telecommunications industry. This approach consists of assembling the packaged, discrete optical, opto-electronic, and electronic components into modules and interconnecting the various discrete components with miniature optical components mated to the output fiber. The advantage of this approach is that the technology utilized is well established and proven, thereby ensuring reliable products that perform in a well-understood fashion. The disadvantage of this approach is the high cost of assembly due to the very precise alignment needed between the optical components and fiber.
A second approach involves the use of hybrid integration technologies such as silicon optical bench (SiOB) and planar light circuits (PLCs). In this approach, the various components are mounted in die form directly onto a silicon carrier that contains both the optical and electrical interconnections among the components. The optical functions that may be integrated onto the silicon carrier include fiber alignment trenches, passive waveguides, splitter/combiners wavelength division multiplexers, reflectors, lenses, etc. Precision pick and place at the silicon carrier wafer level can be used to assemble these units in large volumes. A substantial reduction in both size and cost of a transceiver can be realized with this approach. Additionally, it offers a significant amount of flexibility in the design and type of functionality that can be incorporated onto the silicon substrate.
While commonly used, each of these various FTTX transceiver fabrication processes present various cost and performance consideration in certain applications. For example, active fiber to waveguide alignment and packaging, which is used in many transceiver packaging approaches, is a relatively expensive and time consuming process. Additionally, losses in the typical fiber-to-waveguide coupling can be in the range of 1.0 to 1.5 dB for a typical fiber semiconductor waveguide coupling, assuming the use of a common spot size converter (SSC). Yet another consideration is the overall fabrication cost associated with the typical epi regrowth processes that may be needed to create the desired structures of the integrated transceiver.
Another consideration, particularly with the planar approaches, is the continued problems associated with optical crosstalk, generated by the various components that comprise the FTTX transceiver. Depending on the specific device, the level of crosstalk between the 1.3 micron source and the 1.55 micron receiver of the transceiver can be the limiting factor in certain applications. Finally, the special manufacturing steps and costs associated with the assembly and alignment of discrete components can be quite costly and undesirable in many high volume production situations.
In view of the foregoing, it should be appreciated that there is still a need for an efficient, cost effective method and apparatus for providing FTTX transceivers in fiber optic communication networks. The present invention provides such a transceiver while minimizing the undesired effects of crosstalk between components.
In addition, the present invention addresses other FTTX transceiver deficiencies that are not expressly or inferentially addressed in this background of the invention or the following detailed description of the drawings. Furthermore, additional desirable features provided by the present invention will become apparent to one of ordinary skill in the art from this background of the invention, drawings, detailed description of the drawings, claims and abstract.